When you're ready to deploy VDI but you've got tons of PCs sitting on users' desks, you can turn those PCs into thin clients. But you have to do it the right way, otherwise you'll see fewer benefits of VDI.
The existing estate of desktop PCs and laptops is often a major consideration with virtual desktop infrastructure (VDI) deployments. In some companies, there is thousands of dollars' worth of hardware sitting on workers' desks, and when you're ready to deploy VDI, the hardware isn't always ready to be written off or returned from its lease. The new desktops are shiny virtual machines living in the data center, but what do you do with the old PCs?
A poor PC to thin client conversion will negate operational benefits of VDI.
A quick Internet search of what to do with old PCs leads to suggestions such as turning them into home servers or media centers, but neither of those are for business uses. Usually, companies can turn the PCs into thin clients until they can be retired, which is how many shops defer the Capex of thin clients to the year after the Capex for data center VDI. But the way you turn an old PC into a thin client will determine whether you get thin client benefits. A poor PC to thin client conversion will negate any operational benefits from your VDI deployment.
PC to thin client conversion best practices
The simplest way to make a PC into a thin client is to install your VDI client and put a shortcut on the desktop. This will give users access to their VDI desktop without removing their pre-VDI access. It's a quick, easy and cheap conversion, but a dirty solution that leaves behind the old PC. Nothing stops employees from using their old PCs exactly the way they always have, which means you need to maintain the old desktop PC as well as the new VDI desktop. Unless you remove the ability to get work done using the PC, you still need to support that PC.
To take away the user's access to the PC, you'll have to make the VDI client the only thing on the PC. There are a few applications around that will replace the usual Windows Explorer shell with something that provides the VDI client. These often still require that the user log on to the PC, but that logon also launches the VDI client. Shell replacement makes the local applications unavailable to the user; only the VDI desktop is visible. This is the least you can do to ensure that everyone uses their VDI desktop.
The down side is that you still have a normal operating system on the PC, so you'll still need antivirus software and you'll have to deploy patches. Also, workers are still using a full PC, so all the hardware that supported Windows is still in use. If a hard disk fails, you will need to find a replacement, and then power consumption will be hundreds of watts, rather than tens of watts as is the case with a thin client.
To get some of the support benefits of thin clients, you need to strip down the software inside the device on the user's desk. You can do this with thin client conversion tools which use a thin client operating system in place of Windows on existing PCs. Naturally, this works best if the thin client vendor you have selected for when you replace the PCs also provides a PC conversion tool.
With conversion tools, you can deploy a thin client OS onto the existing hard disk, allowing thin client management tools to manage the device. This removes the patching and antivirus update requirements, and it allows a single tool to manage old PC hardware and new thin clients. Putting a new OS onto old hardware is a fairly simple process and you can usually apply it to a large population of desktop PCs quickly. The downside of turning PCs into thin clients in software-only is that all the old PC hardware is still on the desk in front of the user. If the hardware is old, then it may be prone to failure, which means you'll have to make desk-side parts replacements.
There are also conversion tools that replace the PC hard disk with a flash-based boot media. Some thin client vendors ship their PC conversion tool as a piece of hardware, typically a small Disk-On-Module (DOM) that plugs into the disk controller in place of the old hard disk.
The DOM becomes the boot disk and holds the thin client operating system. DOM-based methods to turn a PC into a thin client take a bit more deploying because you need to open every PC's case to unplug the old hard disk and install the DOM. The benefit is that the old hard disk doesn't consume power and isn't at risk of failing, so it's unlikely you'll need to return to users' desk. Even better, you can deploy many of the software-only thin client conversion tools onto a DOM. Even if your thin client vendor doesn't ship on DOM you can still remove hard disks.
Different ways of converting a PC to a thin client bring different benefits. It will cost more at the start to make the PC more thin-client like, paying off over time as support costs decrease. Always keep in mind that converting a PC to a thin client does not give the PC an infinite lifetime. Expect to replace the hardware before its failure rate becomes high. The ultimate thin client is one designed from the start for no other purpose. Repurposing PCs is only an interim measure.